Call it an ominous, violent, slow-moving science-fiction art film. Call it a study of class structure and a tale of people trying to claw their way from the bottom to the top. Call it an exciting sci-fi thriller. Sorry, there’s no easy way to pigeonhole this English-language movie from Korean writer-director Joon-ho Bong, except to say that it’s a true original.

That can also be said of the filmmaker’s previous two releases on American shores: the monster movie “The Host” and the mystery “Mother.” His singular vision is on display again in “Snowpiercer,” which tells of the scientific community’s solution to a certain environmental crisis: disperse the cooling substance CW7 into the atmosphere and global warming will be fixed.

Well, no, there was a problem. The whole world froze, and all life became extinct, except for a group of lucky survivors who were chosen by lottery and then divvied up into different class groups and shunted aboard a specially designed train that circles the frozen planet once a year, its passengers subsisting in its self-contained environment.

The rich are up front, living in old-style train-travel comfort; the poor are in back, getting by in baggage. All sorts of segments of society are in the long stretch of cars in the middle. (One is filled with ax-wielding ninjas; another has disco partiers.) An armed military tries to keep order. Way up at the very front, according to legend, is the train’s designer, Wilford, who whispered voices call “the divine keeper of the sacred engine.”

This is all taking place 18 years after the world, as the passengers knew it, ended. The poor people in the back, their faces dirty and their clothing drab. They only get to eat a mysterious substance called protein block. (Don’t worry, it’s not Soylent Green, but it’s not much less disgusting.) Under the de facto leadership of Curtis (an initially unrecognizable Chris Evans), they are moving forward a car at a time, hoping to find a better life. Revolts, we’re told, have been attempted before, but have been quashed by the military. Now, though, there’s a rumor that the soldiers’ guns are empty, having long ago run out of bullets.

The first quarter of the film is uncomfortably claustrophobic, not just because the quarters are so tight and the lighting so low – the first peek through a window at the frozen wastelands of dead cities and huge, icy mountains comes about a quarter of the way in – but because cameras are kept so close to people’s faces, it’s sometimes hard to figure out who they are, what they’re doing, and what’s going on around them.

Page 2 of 2 - But it’s easy to understand that the people in back just want to be up front. They want more of the water that’s available to the well-off people (processed from the plentiful ice outside), they want the comfort of real chairs instead of wooden benches and floor space, and they want to be able to eat sushi instead of protein block. (Yes, there’s an aquarium and a sushi bar way up there.)

That would all be nice, but what Curtis wants, or at least what others convince him he wants, is to confront the bossman Wilford (Ed Harris) and to take over the engine which, in this self-contained environment, would mean ruling the world.

The problems are plentiful, though. The people in charge have a mantra about keeping things in order, and they are ready to mete out some really dastardly punishment to those who don’t follow the rules. There’s also the dilemma of people addicted to the hallucinatory drug Kronole, which is made from industrial waste. The revolutionaries must also deal with Wilford’s vicious right-hand woman, Mason (an entirely unrecognizable Tilda Swinton, joyously overacting and adorned with Coke-bottle glasses and buck teeth).

But as the film moves forward, so do the poor, making their way through train cars with accoutrements that get more and more civilized. It’s a simple story simply told, as if the tale itself was just a train moving along a track. Toward the end, the script and its characters start to let loose with back stories and secrets that make everything more complicated but never take away from the mood. The film’s haunting last shot will undoubtedly split viewers and get them into discussions as to whether the ending is upbeat or downbeat.